Even small internal combustion engines, for example for use on motorcycles, scooters, snowmobiles or the like are coupled to dynamo electric machines of the three-phase alternating current generator type, the output of the alternator being controlled by a voltage regulator as well known in connection with automotive-type alternators to supply current to loads which may include a battery. Three-phase alternators for use on motorcycles or the like are subject to substantial shock and vibration. The armature, usually on the stator of the alternator, is wound in three-phase winding, operated either in star or delta connection. The rotor has a field winding thereon, the current through which is controlled by the voltage regulator in order to control the output voltage derived from the three-phase alternator. The output voltage is rectified in a suitable bridge rectifier for supply of current to loads at a substantially level output voltage.
The rotor is usually so constructed that a cylindrical core has a toroidal field winding wound thereon. To form the respective magnetic poles of the field winding, interdigited pole shoes are connected to the end portions of the essentially cylindrical pole core. The overall assembly of pole core, winding thereon, and interdigited or claw pole shoes which extend from the axial end together form the rotor construction. This rotor construction can be supported in bearings specially arranged therefor on the shell, for example the end bells of the alternator; in other constructions, the rotor is formed with an engagement surface, for example a tapering bore or a tapering stub which fits directly on the output shaft of the prime mover--for example a motor cycle engine crankshaft--to be supported entirely by the bearings of the prime mover itself. The rotor can be connected to any prime mover which may also be a shaft on transmission gearing or other source of rotary energy. The field current through the winding is conducted thereto by means of brushes which engage slip rings on the rotor, the current intensity itself being controlled by a suitable voltage regulator.
Rotors of this type which are essentially directly driven from a prime mover, and particularly if journalled in a remote bearing, are frequently subject to substantial vibration and shock; the rotor assembly must be so constructed that it is resistant to all such vibrations and shocks and, additionally, is resistant to rotary oscillations. It has been found that, particularly in remotely journalled rotors, the field winding may loosen with respect to the rotor core; this will, eventually, lead to break of the connecting wires and thus failure of the entire alternator itself. These difficulties are particularly apparent when rotors are remotely journalled and connected to motorcycle engines since the vibration, rotary oscillation, and shock loading of dynamo electric machines used on motorcycles are particularly severe. Additionally, wide swings in temperature and temperature gradients within the dynamo electric machine itself places substantial requirements of mechanical strength on the alternator structure.
It has previously been proposed to utilize separate winding forms to place the field structure on the rotor and to anchor the field structure thereto. Winding forms coupled with insulating disks have been used; still, however, the integrity of the overall rotor construction required for application under extreme conditions of temperature gradients, vibration and shock could not be obtained.